The Trump First Doctrine

Putin respects strength but Trump showed weakness.

Donald Trump left for Europe a week ago with his reputation enhanced by a strong Supreme Court nomination. He returned Monday with that reputation diminished after a tumultuous week of indulging what amounts to the Trump First Doctrine.

Mr. Trump marched through Europe with more swagger than strategy. His diplomacy is personal, rooted in instinct and impulse, and he treats other leaders above all on how much they praise Donald J. Trump. He says what pops into his head to shock but then disavows it if there’s a backlash....